The present invention relates to a method for the leak-tightness and operational testing of a stop valve of a pneumatic suspension of a motor vehicle, with a gas spring supporting a wheel relative to the vehicle body in each case at least on one axle, and with at least in each case one active volume capable of being connected via the stop valve, the pneumatic system and the chassis including at least one connectable pressure source, at least one connectable pressure sink and, for each axle, at least one measuring device directly or indirectly determining the distance between the axle and the vehicle body, and also damping elements limiting the stroke of the respective gas spring.
In a motor vehicle equipped with a pneumatic suspension, gas springs are arranged on one or more axles between the vehicle body and the links or axle parts guiding or carrying the wheels.
The spring action of a pneumatic suspension is determined essentially by the spring rigidity of the gas springs, for example, of the air springs. The spring rigidity is dependent, inter alia, on the enclosed gas volume, the effective cross-sectional area of the compressed volume, the internal pressure and, if appropriate, the compressibility of the pneumatic medium. The greater the enclosed volume and the lower the internal pressure, the lower the spring rigidity and the softer the spring. The enclosed volume is designated hereafter as the active volume.
Pneumatic suspensions in which the individual gas springs have a spring rigidity variable with the aid of a stop valve are commercially available. The spring rigidity is then set harder or softer, depending on the driving conditions. In order to achieve a soft suspension, a gas spring is connected together with an additional-volume vessel. If hard suspension is to be achieved, the connection between the two volumes is separated. In addition, the gas springs of these suspensions are often associated with level control systems, with the aid of which the vehicle body can be raised or lowered, depending on the load or on the conditions of use. In this case, the volume additionally necessary in the event of a rise in level is provided by a pressure source.
If the connection of the individual gas spring together with a corresponding additional-volume vessel does not occur reliably, the individual gas springs may have different spring rigidities. This is detrimental to the driving comfort of the vehicle. The cause of unreliable functioning may be, for example, a malfunction in the activation of the valve or a leak. To prevent such a malfunction, the valves have to be regularly tested. This is performed, for example, by dismounting the valve and testing it on a test stand. This is complicated and requires additional measuring and testing instruments.
It is an object of the present invention to provide a method for leak-tightness and operational testing, which may be performed in a time-saving manner and without additional outlay in terms of measuring means.
The above and other beneficial objects of the present invention are achieved by providing a method as described herein. In one example embodiment of the method according to the present invention, in a first step, with the stop valve open, a stroke, during which at least one damping element is compressed, is set on the individual gas spring. In a second step, after the closing of the stop valve, the individual gas spring is set to a part-stroke of its total stroke between the damping elements. In a third step, after the opening of the stop valve, the distance which is established between the axle and the vehicle body is determined with the aid of the measuring device and is compared with a predetermined desired value.
According to another example embodiment of a method according to the present invention, in a first step, with the stop valve open, the individual gas spring is set to a part-stroke of its total stroke between the damping elements. In a second step, after the closing of the stop valve, a stroke, during which at least one damping element is compressed, is set on the individual gas spring. In a third step, after the opening of the stop valve, the distance which is established between the axle and the vehicle body is determined with the aid of the measuring device and is compared with a predetermined desired value.
In the first method described above, with the stop valve open, the same pressure prevails in the entire active volume of a gas spring and in its connectable active volume. The pressure in the active volumes falls or rises as a result of the compression of at least one damping element limiting the contraction or expansion stroke of the gas spring. In the second step, after the separation of the volumes by the respective stop valve, the pressure is maintained in the connectable active volume, while the pressure is increased or reduced in the individual gas spring, with the respective damping element being relieved at the same time. In the third step, pressure compensation between the gas spring and the additional-volume vessel occurs as a result of the opening of the stop valve.
In the second method described above, in the first step, pressure compensation is produced in the entire active volume of the gas spring and of the additional-volume vessel. In the second step, the pressure is mentioned in the connectable active volume, while the pressure is increased or reduced in the individual gas spring by load being exerted on a damping element. In the third step, pressure compensation between the gas spring and the connectable active volume occurs as a result of the opening of the stop valve.
If the level change of the vehicle body which is established after the opening of the stop valve deviates from a predetermined desired-value change, there is a malfunction of, for example, the stop valve.
The test of operational leak-tightness may be performed, without the dismantling of components, by the devices already present in the vehicle. This test saves time and requires a low outlay in terms of assembly.
The pressure source may in this case be, for example, a compressor or a pressure accumulator. The pressure sink may be the free surroundings downstream of a discharge valve.
The measuring device may be, for example, a level-measuring instrument, a sensor or a body acceleration sensor.
A measuring device of this type may be arranged, for example, on each axle or on each wheel.
The subassembly described as a gas spring may also include two or more parallel-connected or series-connected individual springs.
The suspension may also be filled at least partially with a liquid, instead of with a gas, for example, air. This medium may be incompressible. In order to achieve a spring action, for example, a diaphragm, if appropriate in a compensating tank, is arranged on each of the springs.
The valves arranged in the connecting lines between the springs may be activated centrally. For this purpose, for example, the valves may have electromagnetically actuated coils. These may be connected to a control unit and be influenced by the latter.
Further details of the invention may be gathered from the following description of a schematically illustrated example embodiment.